Power generator

ABSTRACT

A power generator that operates at a reduced temperature level includes a flux shunt that reduces the amount of fringing magnetic flux axially impinging upon a stator, flange, and multiple keybars during operation of the generator. By reducing the amount of axially impinging flux, the flux shunt reduces an operating temperature of the stator and flange and reduces a voltage differential between keybar voltages induced by the flux in the multiple keybars.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. patent applicationSer. No. 09/749,197, filed Dec. 27, 2000, the entire contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The invention relates generally to a power generator, and inparticular to a reduction of heat dissipation and undesirable voltagedifferentials in a power generator.

[0003] Thermal issues are critical to the design of a high powerelectrical generator and can serve as limiting factors in generatoroperation. A typical design of a high power electric generator includesa rotor having rotor windings rotatably disposed inside of a statorhaving stator windings. The rotation of the rotor induces anelectromagnetic field in the stator, which electromagnetic field in turninduces a current in, and voltage drop across, the stator windings.However, the electromagnetic field also induces eddy currents in thestator, which is magnetically and electrically resistive. The eddycurrents cause the dissipation of energy in the stator in the form ofheat and impose a thermal constraint on the operation of the generator.

[0004] In order to improve generator efficiency and reduce generatorsize, generator manufacturers are constantly endeavoring to improve thethermal performance of the generator. For example, a prior art design ofa high power electrical generator 100 is illustrated in FIGS. 1, 2, and3. FIG. 1 is a cross-sectional view of generator 100 from an isometricperspective. FIG. 2 is a cut-away view of generator 100 along axis 2-2.As shown in FIGS. 1 and 2, electrical generator 100 includes asubstantially cylindrical stator 102 having a stator core 104 andhousing a substantially cylindrical rotor 110. Multiplecircumferentially distributed and axially oriented keybars 118 arecoupled together at each of a proximal end and a distal end by one ofmultiple flanges 204 (not shown in FIG. 1). Each keybar 118 is coupledto an outer surface of stator 102. The multiple keybars 118, togetherwith the multiple flanges 204, form a keybar cage around the stator 102.

[0005] An inner surface of stator 102 includes multiple stator slots 106that are circumferentially distributed around an inner surface of stator102. Each stator slot 106 is radially oriented and longitudinallyextends approximately a full length of stator 102. Each stator slot 106receives an electrically conductive stator winding (not shown).

[0006] Rotor 110 is rotatably disposed inside of stator 102. An outersurface of rotor 110 includes multiple rotor slots 114 that arecircumferentially distributed around the outer surface of rotor 110.Each rotor slot 114 is radially oriented and longitudinally extendsapproximately a full length of rotor 110. An air gap exists betweenstator 102 and rotor 110 and allows for a peripheral rotation of rotor110 about axis 130.

[0007] Each rotor slot 114 receives an electrically conductive rotorwinding (not shown). Each rotor winding typically extends from aproximal end of rotor 110 to a distal end of the rotor in a first rotorslot 114, and then returns from the distal end to the proximal end in asecond rotor slot 114, thereby forming a loop around a portion of therotor. When a direct current (DC) voltage differential is applied acrossa rotor winding at the proximal end of rotor 110, an electrical DCcurrent is induced in the winding.

[0008] Similar to the rotor windings, each stator winding typicallyextends from a proximal end of stator 102 to a distal end of the statorin a first stator slot 106, and then returns from the distal end of thestator to the proximal end of the stator in a second stator slot 106,thereby forming a stator winding loop. A rotation of rotor 110 inside ofstator 102 when a DC current is flowing in the multiple windings ofrotor 110 induces electromagnetic fields in, and a passage of magneticflux through, stator 102 and the loops of stator windings. The passageof magnetic flux in turn induces an alternating current in each statorwinding and eddy currents arid magnetic and resistive losses in stator102.

[0009]FIG. 3 is a side view of a cross-section of generator 100 andillustrates a coupling of magnetic flux 302 from rotor 110 to stator 102as the rotor rotates inside of the stator. Magnetic flux 302 generatedby a rotation of rotor 110 couples to and passes through the surroundingstator 102. Magnetic flux 302 induces a flow of multiple eddy currentsin the magnetically and electrically resistive stator 102, whichcurrents cause energy dissipation and heat generation in the stator thatposes a thermal constraint on the operation and capacity of generator100. As a result, generator designers are always seeking improvedmethods of thermal management for power generator stators.

[0010] One known thermal management technique is the construction ofstator core 104 from multiple ring-shaped laminations 402. FIG. 4 is apartial perspective of generator of 100 and illustrates a typicaltechnique of constructing stator core 104. As shown in FIG. 4, themultiple ring-shaped laminations 402 are stacked one on top of anotherin order to build up stator core 104. Each lamination 402 is dividedinto multiple lamination segments 404. Each lamination segment 404includes multiple slots 120 (not shown in FIG. 4), wherein at least oneslot 120 of each segment 404 aligns with one of the multiple keybars118. Each keybar in turn includes an outer side 124 and an inner, orlocking, side 122 that mechanically mates with one of the multiple slots120. Stator core 104 is then constructed by sliding each laminationsegment 404, via one of the multiple slots 120, into the keybar cageformed by the multiple keybars 118. The coupling of one of the multipleslots 120 of a lamination segment 404 with a locking side 122 of akeybar 118 affixes each lamination segment 404, and thereby eachlamination 402, in position in stator 102. By building stator core 104from stacked laminations, as opposed to constructing a solid core,circulation of a current induced in stator 102 is limited to alamination, thereby restricting current circulation and size andconcomitantly reducing stator heating.

[0011] The above thermal management technique does not fully addressthermal problems caused by a “fringing” of magnetic flux at each end ofstator 102. As illustrated in FIG. 3, the “fringing” 304 of magneticflux at each end of stator 102 results in a number of flux lines 302axially, or normally, impinging upon each end of stator core 104 andupon the multiple flanges 204. A result of the fringing magnetic flux304 is a greater flux density at each end of stator core 104 as comparedto more centrally located portions of the stator core. The greater fluxdensity at each end of stator core 104 results in increased eddycurrents and greater heat dissipation in the laminations of stator core104 near the ends of the stator, as opposed to more centrally locatedlaminations. The fringing effect also results in increased eddy currentsand greater heat dissipation in each flange 204.

[0012] In order to combat a buildup of heat at each end of stator 102due to fringing magnetic flux 304, an inner surface of stator core 104,at each end of the stator core, is radially stepped away 202 from rotor110, as shown in FIGS. 2 and 3. By increasing the distance between rotor110 and stator core 104 at each end of the stator core, an amount offlux axially impinging upon each end of the stator core is reduced.However, the stepping of the ends of stator core 104 away from rotor 110is only a partial solution to the stator core heat dissipation problempresented by “fringing” and does not address the problem of heatdissipation in the multiple flanges 204.

[0013] A portion of the fringing magnetic flux 304 also impinges uponthe ends of each of the multiple keybars 118. The impinging of fringingmagnetic flux upon an end of a keybar 118 can produce an uneven couplingof flux into each keybar, with a greater flux density at a keybar endthan in more centrally located portions of the keybar. The unevencoupling of flux can produce keybar voltages and keybar currents in eachkeybar 118. In “turn, the existence of keybar voltages in each keybar118 can produce keybar voltage differentials between keybars, whichvoltage differentials can be transmitted to the lamination segments 404coupled to the keybars. When a voltage differential is transmitted toadjacent lamination segments 404, the voltage differential can causearcing between the adjacent segments, overheating in stator core 104,and reduced generator 100 performance. The arcing can also createlocalized heating in stator core 104, causing lamination segments 404and lamination rings 402 to fuse together. Such fusing can spreadquickly in generator 100 as the lamination segments 404 and laminationrings 402 short circuit to each other, resulting in damage to thegenerator.

[0014] Therefore, a need exists for a method and apparatus for furtherreducing the heat dissipated in the ends of a stator core and in aflange and for providing for a more uniform coupling of flux into akeybar.

BRIEF SUMMARY OF THE INVENTION

[0015] Thus there is a particular need for a method and apparatus thatreduces the heat dissipated in the ends of a stator core and in a flangeand that provides for a more uniform coupling of flux into a keybar.Briefly, in accordance with an embodiment of the present invention, aflux shunt is provided for insertion adjacent to an inner surface of thestator and approximately at an end of the stator and wherein apermeability of the flux shunt is greater than a permeability of thestator core. The flux shunt reduces the amount of magnetic fluximpinging in an axial direction upon the flanges and upon ends of thekeybars and the stator core. By reducing the impinging flux, the fluxshunt reduces the heat dissipated in the ends of stator and furtherprovides for a more even coupling of flux into a keybar.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is an isometric perspective of an end view of across-section of a power generator of the prior art.

[0017]FIG. 2 is a cut-away view of the prior art power generator of FIG.1 along axis 2-2.

[0018]FIG. 3 is side view of a cross-section of the prior art powergenerator of FIG. 1 and illustrates a coupling of magnetic flux, from arotor of the power generator to a stator of the power generator as therotor rotates inside of the stator.

[0019]FIG. 4 is a partial perspective of the prior art power generatorof FIG. 1.

[0020]FIG. 5 is an end view of a cross-section of an exemplary powergenerator from an isometric perspective in accordance with an embodimentof the present invention.

[0021]FIG. 6 is a cut-away view of the power generator of FIG. 5 alongaxis 7-7 as shown in FIG. 5 in accordance with an embodiment of thepresent invention.

[0022]FIG. 7 is a side view of a cross section of the power generator ofFIG. 5 in accordance with an embodiment of the present invention.

[0023]FIG. 8 is atop view of an exemplary lamination segment inaccordance with an embodiment of the present invention.

[0024]FIG. 9 is a cross-sectional side view of an end of the powergenerator of FIG. 5 in accordance with an embodiment of the presentinvention.

[0025]FIG. 10 is a logic flow diagram of steps executed in order tocontrol flux in a power generator in accordance with an embodiment ofthe present invention.

[0026]FIG. 11 is a logic flow diagram of steps executed in order toreduce a keybar voltage of a power generator in accordance with anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0027] Referring now to FIGS. 5, 6, and 7, an exemplary power generator500 that operates at a reduced stator temperature level and at reducedkeybar voltage differentials is illustrated. FIG. 5 is an isometricperspective of an end view of a cross section of power generator 500.FIG. 6 is a cut-away view of electrical generator 500 along axis 6-6 asshown in FIG. 5. FIG. 7 is a cross-sectional side view of generator 500.Generator 500 includes a substantially cylindrical stator 502 having astator core 504 and housing a substantially cylindrical rotor 510rotatably disposed inside of the stator. Multiple circumferentiallydistributed and axially oriented keybars 518 are coupled together ateach of a proximal end and a distal end by one of multiple flanges 604(not shown in FIG. 5). Each keybar 518 is coupled to an outer surface ofstator 502. The multiple keybars 518, together with the multiple flanges604, form a keybar cage around the stator 502.

[0028] An inner surface of stator 502 includes multiple stator slots 506that are circumferentially distributed around the inner surface of thestator. Each stator slot 506 is axially oriented and extendsapproximately a full length of stator 502. Each stator slot 506 receivesan electrically conductive stator winding (not shown). Between each pairof adjacent stator slots 506 is a stator tooth 508 that, similarly, iscircumferentially distributed around the inner surface of stator 102 andextends approximately a full length of stator 502. Each stator tooth 508is radially oriented and extends radially inward toward rotor 510 fromstator 502.

[0029] Similar to stator core 104 of the prior art, stator core 504preferably includes multiple, stacked ring-shaped laminations that areeach divided into multiple lamination segments. FIG. 8 is a top view ofan exemplary lamination segment 800. Lamination segment 800 includes ayoke 802 and one or more stator teeth 804. Between each pair of statorteeth 804 is a stator slot 806. Each lamination segment 800 furtherincludes multiple dovetail-shaped slots 808 in an outer edge of thesegment for mechanically coupling the lamination segment to one or morekeybars 518. In turn, each keybar 518 includes an outer side and aninner, locking side 810. Locking side 810 includes a dovetail-shapedridge that extends a length of the keybar and that is designed to matewith a dovetail-shaped slot 808 of a lamination segment 800. Eachring-shaped lamination, and each lamination segment 800 associated withthe lamination, is fixed in position in stator 502 by sliding eachlamination segment 800 of the ring-shaped lamination onto a keybar 518via the dovetail-shaped slots 808 and the corresponding dovetail-shapedridge of the keybar. Multiple flanges 604 then hold the multiple keybars518 and, in association with the keybars, the multiple ring shapedlaminations in position in stator core 504.

[0030] Rotor 510 is rotatably disposed inside of stator 502. Similar torotor 110 of the prior art, rotor 510 has an outer surface that includesmultiple rotor slots 514, which slots 514 are circumferentiallydistributed around the outer surface of rotor 510. Each rotor slot 514is radially oriented and extends approximately a full length of rotor510. Between each pair of adjacent rotor slots 514 is a rotor tooth 516that similarly is circumferentially distributed around the inner surfaceof rotor 510 and extends approximately a full length of rotor 510. Eachrotor tooth 516 is radially oriented and extends radially outward towardstator 502 from rotor 510. An air gap exists between stator 502 androtor 510 that allows for a peripheral rotation of rotor 510 about axis520.

[0031] The multiple flanges 604 are each disposed adjacent to an end ofstator core 504. Disposed between each flange 604 and stator core 504 isan outside space block 606. Each of the multiple flanges 604 is aring-shaped metallic material that includes multiple keybar studapertures (not shown) for receiving a keybar stud 608. The apertures arecircumferentially disposed around each flange 604 in positions thatcorrespond to positions of keybars 518 around stator 502. Each end ofeach keybar 518 includes a threaded keybar stud 608 that extends axiallyoutward from the end of the keybar. Each flange 604 is placed on an endof stator 502 and over the keybar studs 608 such that each stud extendsthrough the flange via a corresponding keybar stud aperture. Each flange604 is then mechanically fastened onto an end of stator 502 and themultiple keybars 518 by multiple threaded nuts 610 that are each screwedonto a correspondingly threaded keybar stud 608.

[0032] Similar to generator 100 of the prior art, each slot of themultiple rotor slots 514 receives an electrically conductive rotorwinding (not shown) and each slot of the multiple stator slots 506 ofgenerator 500 receives an electrically conductive stator winding (notshown). Each rotor winding typically extends from a proximal end ofrotor 510 to a distal end of the rotor in a first rotor slot of themultiple rotor slots 514, and then returns from the distal end to theproximal end in a second rotor slot of the multiple rotor slots 514,thereby forming a loop around a portion of the rotor. Similar to therotor windings, each stator winding typically extends from a proximalend of stator 502 to a distal end of the stator in a first stator slotof the multiple stator slots 506, and then returns from the distal endof the stator to the proximal end of the stator in a second stator slotof the multiple stator slots 506, thereby forming a stator winding loop.

[0033] A rotation of rotor 510 inside of stator 502 when a DC current isflowing in the multiple windings of rotor 510 induces magnetic fieldsin, and a passage of magnetic flux through, stator 502 and the loopsformed by the stator windings. The passage of magnetic flux through thestator winding loops induces a current in the stator windings and acorresponding power generator output voltage. The rotation of rotor 510also induces a “fringing” of the magnetic flux at each end of stator502. In order to combat a buildup of heat due to fringing, an innersurface of stator core 504 includes multiple steps 602 that radiallystep the stator core away from rotor 510 at each end of the stator core.However, the radial stepping 602 alone does not fully prevent anundesirable buildup of heat at each end of stator core 504. Furthermore,the radial stepping 602 does not address the issue of “fringing” fluximpinging upon each of the multiple flanges 604 or upon the ends of eachof the multiple keybars 518. In order to further reduce the heat buildupand to reduce the impinging of “fringing” flux upon the keybars 518 andflanges 604, power generator 500 includes multiple flux shunts 522 thatattract, and thereby redistribute, the fringing magnetic flux.

[0034] Each flux shunt 522 provides a low reluctance path for thefringing magnetic flux produced by a rotation of rotor 510. By providinga low reluctance path, each flux shunt 522 attracts the fringingmagnetic flux that would otherwise axially impinge upon a flange 604 andupon an end of each of stator core 504 and multiple keybars 518. Thefringing magnetic flux is thereby redirected from the flanges 604,stator core 504, and the multiple keybars 518 to the shunt 522. Byredirecting the fringing magnetic flux, each flux shunt 522 reduces thecurrent induced in, and concomitantly the energy and heat dissipated in,stator core 504 and flanges 604 by the fringing flux. Furthermore, byredirecting the fringing magnetic flux, each flux shunt 522 reduces thefringing flux coupling into an end of each keybar 518 and provides for amore uniform coupling of magnetic flux into the keybar. A more uniformcoupling of magnetic flux into each keybar 518 reduces a likelihood ofan induction of keytbar voltages and keybar currents in the keybar andreduces a development of keybar voltage differentials between each ofthe multiple keybars.

[0035] Preferably, each flux shunt 522 includes a magnetically isotropicmaterial that is electrically highly resistive and thermally conductiveand that has a higher axial permeability than stator core 504. Forexample, a flux shunt 522 may include a powdered iron composition,wherein the powdered iron composition is electrically highly resistiveand thermally conductive, has a high isotropic permeability, and, duethe to powdered nature of the composition, will produce minimal currentand low losses when a magnetic field is applied to the composition.Those who are of ordinary skill in the art realize that other highresistance, high isotropic permeability materials or compounds may beused in flux shunt 522 without departing from the spirit and scope ofthe present invention.

[0036] Each flux shunt 522 has a radially outer surface that is disposedadjacent to the inner surface, or teeth 508, of stator 502 and aradially inner surface that is disposed opposite rotor 510. Preferably,each flux shunt 522 is further disposed in a section of stator 502, orstator core 504, that is radially stepped away 602 from rotor 510. Inone embodiment of the present invention, a flux shunt of the multipleflux shunts 522 is disposed at a proximal end of stator 502, or statorcore 504, and another flux shunt of the multiple flux shunts 522 isdisposed at a distal end of the stator. However, in alternativeembodiments of the present invention, flux shunt 522 may be inserted ateither the proximal end of stator 502 or at the distal end of thestator. Furthermore, each flux shunt 522 is disposed in a manner suchthat the flux shunt does not obstruct the passage of the stator windingsthrough stator core 504.

[0037] In one embodiment of the present invention, a flux shunt 522 maybe substantially cylindrically-shaped and disposed adjacent to the innersurface of stator 502 at approximately an end of the stator. Preferably,flux shunt 522 is radially stepped outward to mate with the multiplesteps of a stepped region 602 of stator 502. In another embodiment ofthe present invention, a flux shunt 522 may include multiple discreterings that are each disposed adjacent to the inner surface of stator 502and that each fits into one of the multiple steps included in eachstepped region 602. In yet another embodiment of the present invention,a flux shunt 522 may include multiple segments that are discretelydisposed around the periphery of the inner surface of stator 502, whichsegments may each mate with one or more steps of the multiple steps of astepped region 602 of stator 502. The multiple segments, in combination,may or may not completely encircle the interior of a stepped region 602of stator 502. In still another embodiment of the present invention,each ring or segment included in flux shunt 522 may include aperturesthat allow for the passage of gas through the shunt.

[0038]FIG. 9 is a partial side view of a cross-section of an end ofstator 502 and rotor 510 in accordance with an embodiment of the presentinvention. Also shown in FIG. 9 is a retaining ring 902 and a centeringring 904 that fit over an end of the rotor windings (not shown) and thathold the windings in position as rotor 510 rotates inside of stator 502.In one embodiment of the present invention, flux shunt 522 is retainedin position relative to stator core 504 by a flux shunt retainer 906.Flux shunt retainer 906 is disposed adjacent to the inner surface offlux shunt 522 and is affixed in position relative to stator core 504.Those who are of ordinary skill in the art realize that there are manyways of either removably or permanently affixing flux shunt retainer 906in position relative to stator 502 without departing from the spirit andscope of the present invention. For example, flux shunt retainer 906 maybe fastened by bolts or screws onto outside space block 606 in order tohold flux shunt retainer 906, and thereby flux shunt 522, in positionrelative to stator core 504. By way of another example, flux shuntretainer 906 can be welded to outside space block 606, or outside spaceblock 606 may be milled in such a manner that the outside space blockincludes an inner lip that functions as flux shunt retainer 906.

[0039] Preferably, flux shunt retainer 906 is a substantiallycylindrically-shaped ring that is disposed adjacent to the inner surfaceof flux shunt 522. However, those who are of ordinary skill in the artrealize that flux shunt retainer 906 may include any design intended tohold flux shunt 522 in position relative to stator core 504, such asplates that are circumferentially disposed around the inner surface offlux shunt 522, which plates may be individually axed to stator 502 ormay be linked together to form a flux shunt retainer assembly that isaffixed to stator 502, without departing from the spirit and scope ofthe present invention. Preferably, each plate or the ring included influx shunt retainer 906 is of a length ‘L’ that is sufficient to holdflux shunt 522 in position relative to stator core 504, which length Lmay or may not be of a same length as flux shunt 522. By axing fluxshunt retainer 906 in position relative to stator 502, flux shunt 522 isalso affixed in position relative to the stator.

[0040] In another embodiment of the present invention, flux shunt 522may be directly axed to outside space block 606 instead of using fluxshunt retainer 906. For example, flux shunt 522 may be attached tooutside space block 606 by an adhesive or may be mechanically fastenedto the outside space block by a fastener such as a bolt or a screw. Inyet another embodiment of the present invention, flux shunt 522 insteadmay be axed to stator core 504, preferably by an adhesive oralternatively by a mechanical fastener. The means used to affix fluxshunt 522 in position relative to stator 502 is not critical to thepresent invention, and other means of affixing the flux shunt inposition relative to the stator may occur to those of ordinary skill inthe art without departing from the spirit and scope of the presentinvention.

[0041] By including multiple flux shunts 522 that are each disposedadjacent to an inner surface of stator 502, power generator 500 iscapable of operating at a lower temperature and at reduced keybarvoltage differentials relative to the prior art. Each flux shunt 522 isdisposed at either a proximal end of stator 502 or a distal end of thestator. Each flux shunt 522 has a high permeability and a low reluctancein all directions and attracts the fringing magnetic flux at the end ofstator 502, redirecting the flux away from a flange 604 and from theends of each of stator core 504 and the multiple keybars 518. Byredirecting the fringing flux, each flux shunt 522 reduces eddy currentsinduced in, and energy and heat dissipated in, a flange 604 and ends ofstator core 504 and multiple keybars 518 by the fringing flux, resultingin a more efficient power generator. Also, since stator core and flangetemperatures can serve as operating constraints for power generators, areduction of the operating temperatures of the stator core and flangefor a given rotor 410 winding current can allow for the power generatorto be operated at a higher rotor winding current and a higher outputvoltage.

[0042] In addition, by redistributing the fringing flux, each flux shunt522 reduces the fringing flux impinging upon an end of each keybar 518and causes a more uniform distribution of flux in the keybar. A moreuniform distribution of flux in a keybar reduces the likelihood ofkeybar voltages and also reduces a likelihood of voltage differentialsdeveloping among the multiple keybars 518. By reducing the likelihood ofvoltage differentials, power generator 500 reduces a possibility ofarcing in the stator core due to voltage differentials among laminationscoupled to the keybar.

[0043] Furthermore, the multiple flux shunts 522 in power generator 500are positioned in areas where only air gaps existed in the prior art.The inclusion of a flux shunt 522 where only an air gap previouslyexisted results in an induction of an increased amount of magnetic fluxand an increased output voltage for a given level of operation of powergenerator 500. Alternatively, the inclusion of a flux shunt 522 whereonly an air gap previously existed reduces the rotor winding currentrequired to produce a given output voltage, resulting in a moreefficient power generator.

[0044]FIG. 10 is a logic flow diagram 1000 of a method for controllingflux in a power generator in accordance with an embodiment of thepresent invention. Preferably, the power generator includes anapproximately cylindrical stator having an inner surface, an outersurface, and a stator core, and a rotor rotatably disposed inside of thestator. The power generator further includes multiple axially orientedkeybars that are circumferentially disposed around the outer surface ofthe stator and multiple flanges that are each disposed at an end of thestator. The logic flow begins (1001) when a flux shunt is positioned(1002) adjacent to the inner surface of the stator and at approximatelyan end of the stator. A rotating (1003) of the rotor induces (1004) afringing magnetic flux at the end of the stator. The fringing magneticflux is attracted (1005) to the flux shunt, and the logic flow ends(1006). The attraction of the fringing magnetic flux to the flux shuntresults in a reduction of the amount of fringing magnetic flux thatwould otherwise axially, or normally, impinge upon the ends of thestator core and the multiple keybars and upon a flange of the multipleflanges.

[0045] By attracting (1005) the fringing flux to the flux shunt andredirecting fringing flux away from the stator core, flange, andkeybars, the present invention reduces eddy currents and energy and heatdissipation in each of the stator core, flange, and keybars, resultingin a more efficient power generator. In addition, reduction of an amountof fringing magnetic flux impinging upon an end of each keybar causes amore uniform distribution of flux in the keybar, reduces the likelihoodof keybar voltages, and reduces a likelihood of voltage differentialsdeveloping among the multiple keybars 518. Furthermore, when a fluxshunt is positioned (1002) in areas of a power generator where only airgaps existed in the prior art, an increased amount of magnetic flux maybe induced for a given level of operation of the power generator. Anincreased amount of magnetic flux results in an increased voltageinduced by the flux in the stator windings, which in turn reduces therotor winding current required to produce a given voltage and produces amore efficient power generator.

[0046]FIG. 11 is a logic flow diagram 1100 of a method for reducing apower generator keybar voltage differential in accordance with anotherembodiment of the present invention. Preferably, the power generatorcomprises an approximately cylindrical stator having an inner surface,an outer surface, and a stator core. The power generator furthercomprises multiple keybars axially disposed adjacent to the outersurface of the stator and a rotor rotatably disposed inside of thestator. The logic flow begins (1101) when a flux shunt is positioned(1102) adjacent to the inner surface of the stator and approximately atan end of the stator. A rotating (1103) of the rotor induces (1104) afirst keybar voltage in a first keybar of the multiple keybars andfurther induces (1105) a second, different keybar voltage in a secondkeybar of the multiple keybars, producing (1106) a voltage differentialbetween the first keybar voltage and the second keybar voltage. Thevoltage differential is less than a voltage differential that wouldexist between keybar voltages induced in each of the first and secondkeybars by a rotation of the rotor in the absence of the flux shunt. Thelogic flow then ends (1107).

[0047] In sum, a power generator is provided that includes multiple fluxshunts that each reduces an amount of flux coupling into a stator,flange and into multiple keybars of the power generator during operationof the generator. By reducing the amount of flux coupling into a statoror flange, the power generator is able to operate at a reducedtemperature level, or alternatively can be driven harder in order tooperate at the same temperature level. By reducing the amount of fluxcoupling into the multiple keybars, a voltage differential betweenkeybar voltages induced by the flux in each of the multiple keybars isreduced, reducing the potential for arcing and localized heating in thestator.

[0048] While the present invention has been particularly shown anddescribed with reference to particular embodiments thereof, it will beunderstood by those skilled in the art that various changes may be madeand equivalents substituted for elements thereof without departing fromthe spirit and scope of the invention. In addition, many modificationsmay be made to adapt a particular situation or material to the teachingsof the invention without departing from the essential scope thereof.Therefore, it is intended that the invention not be limited to theparticular embodiments disclosed herein, but that the invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A power generator comprising: a rotor having aradial outer surface; a stator assembly comprising: an approximatelycylindrically-shaped stator core comprising an outer surface, a radialinner surface, and two ends; and a flux shunt circumferentially disposedadjacent to the inner surface of the stator core at approximately an endof the two ends of the stator core, the flux shunt having a convex outersurface disposed adjacent to the radial inner surface of the stator coreand a concave inner surface disposed adjacent to the radial outersurface of the rotor; and a plurality of axially oriented keybarscircumferentially disposed adjacent to the outer surface of the statorcore; wherein the rotor is rotatably disposed inside of the stator. 2.The power generator of claim 1, wherein the flux shunt causes themagnetic flux axially impinging upon the ends of the keybars to be lessthan a magnetic flux that would axially impinge upon the ends of thekeybars in the absence of the flux shunt.
 3. A power generatorcomprising: a stator having a radial inner surface; and a flux shuntdisposed adjacent to the inner surface of the stator, the flux shunthaving a convex outer surface disposed adjacent to the radial innersurface of the stator.
 4. The power generator of claim 3, wherein theflux shunt comprises a magnetically isotropic material.
 5. The powergenerator of claim 4, wherein the magnetically isotropic materialcomprises powdered iron.
 6. The power generator of claim 3, wherein theflux shunt is substantially cylindrically-shaped.
 7. The power generatorof claim 3, wherein the flux shunt comprises multiple discrete ringsdisposed around the periphery of an inner surface of the stator.
 8. Thepower generator of claim 3, wherein the flux shunt comprises a pluralityof segments discretely disposed around the periphery of the innersurface of the stator.
 9. The power generator of claim 3, wherein theflux shunt comprises a first flux shunt disposed at a first end of thestator, and the power generator stator assembly further comprises asecond flux shunt disposed adjacent to the inner surface of the statorat a second end of the stator.
 10. The power generator of claim 3,wherein the inner surface of the stator comprises multiple stepsstepping the stator away from a rotor, and wherein the flux shunt outersurface mates with the multiple steps of the stator.
 11. The powergenerator of claim 3, wherein the flux shunt is formed from anelectrically resistive, thermally conductive, and magnetically permeablematerial.
 12. The power generator of claim 3, further comprising a fluxshunt retainer disposed adjacent to the inner surface of the flux shunt.13. The power generator of claim 12, wherein the flux shunt retainer isaffixed to an outside space block disposed at an end of the stator. 14.The power generator stator assembly of claim 3, wherein the statorcomprises opposing axial ends and the flux shunt is disposed at one ofthe opposing axial ends.
 15. The power generator of claim 3, wherein apermeability of the flux shunt is greater than a permeability of astator core of the stator.
 16. The power generator of claim 3, furthercomprising a flange disposed adjacent to an end of the stator, whereinthe rotation of the rotor produces a fringing magnetic flux that axiallyimpinges upon the flange, and wherein the flux shunt causes the magneticflux axially impinging upon the flange to be less than a magnetic fluxthat would axially impinge upon the flange in the absence of the fluxshunt.
 17. A power generator comprising: a stator; a rotor rotatablydisposed within the stator, the rotor having a radial outer surface; aflux shunt disposed adjacent to the inner surface of the stator, theflux shunt having a concave inner surface disposed adjacent to theradial outer surface of the rotor.
 18. The power generator of claim 17,wherein the flux shunt is substantially cylindrically-shaped.
 19. Thepower generator of claim 17, wherein the flux shunt comprises multiplediscrete rings disposed around the periphery of an inner surface of thestator.
 20. The power generator of claim 17, wherein the flux shuntcomprises a plurality of segments discretely disposed around theperiphery of the inner surface of the stator.
 21. The power generator ofclaim 17, wherein the flux shunt is formed from an electricallyresistive, thermally conductive, and magnetically permeable material.22. A power generator comprising: an approximately cylindrically-shapedstator comprising a stator core, an inner surface, and two ends; a fluxshunt circumferentially disposed adjacent to the inner surface of thestator at approximately an end of the two ends of the stator; a rotorrotatably disposed inside of the stator; and wherein a rotation of therotor produces a fringing magnetic flux that axially impinges upon theend of the stator, and wherein the flux shunt causes the magnetic fluxaxially impinging upon the end of the stator to be less than a magneticflux that would axially impinge upon the end of the stator in theabsence of the flux shunt.